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The sample

The sample of the print preview

The article gives a class, CGLMemoryDC, which can support OpenGL printing under Win95/NT

CGLMemoryDC stores the DIB data for the printer context device.

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//data of DIB
private:
	HBITMAP      m_hBitmap;       //handle of bitmap
	BITMAPINFO   m_DIBInfo;       //infomation about the DIB
	BYTE*        m_hImage;        //DIB color data
	DWORD        m_dwDataSize;    //DIB data size 

CGLMemoryDC also gives the functions to get DIB data from selected context device or set DIB data to target context device

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/********************************************************************/
/* Scan the image from the device context   					    */
/********************************************************************/
void CGLMemoryDC::CopyDataFromDC(CDC* pDC, CRect& rect)
{
	CDC      dcBuffer;       //the compatible DC 
	CBitmap  bmBitmap;		 //bitmap in memory for retreive data from DC
	CBitmap* pbmBitmapOld;

	//if the orignal bitmap did not set up
	if(!m_hBitmap)
        return;

	//create compatible DC to copy image
	dcBuffer.CreateCompatibleDC(pDC);

	//create memory bitmap 
	bmBitmap.CreateCompatibleBitmap(pDC,
                  m_DIBInfo.bmiHeader.biWidth,
                  m_DIBInfo.bmiHeader.biHeight);
    
	//set memory bitmap to memory DC
	pbmBitmapOld = dcBuffer.SelectObject(&bmBitmap);
    
	//copy source DC image to memory bitmap
	dcBuffer.StretchBlt(0, 0,  
			m_DIBInfo.bmiHeader.biWidth,
			m_DIBInfo.bmiHeader.biHeight,
			pDC, 
			rect.left,
			rect.top,
			rect.Width(),
			rect.Height(),
			SRCCOPY);

	//restore the orginal object in memory DC
    dcBuffer.SelectObject(pbmBitmapOld);

	//copy image data from memory bitmap
	GetDIBits(pDC->m_hDC,
		HBITMAP)bmBitmap, 
		0, 
		m_DIBInfo.bmiHeader.biHeight,
		m_hImage,
		&m_DIBInfo,
		DIB_RGB_COLORS);
}


/********************************************************************/
/* Copy image data to target DC             					    */
/*                                                                  */ 
/* This function just support the color printer setting in Text     */
/* mode																*/
/********************************************************************/
void CGLMemoryDC::CopyDataToDC(CDC* pDC, CRect& rect)
{
    ::StretchDIBits(pDC->m_hDC, 
			rect.left, 
			rect.top, 
			rect.Width(), 
			rect.Height(),
			0, 0, 
			m_DIBInfo.bmiHeader.biWidth, 
			m_DIBInfo.bmiHeader.biHeight,
			m_hImage,  
			&m_DIBInfo, 
			DIB_RGB_COLORS, 
			SRCCOPY);
}


/********************************************************************/
/* Write image data directly to target DC                           */
/*                                                                  */ 
/* This function just support the color printer setting in Photo    */
/* quality mode                                                     */
/********************************************************************/
void CGLMemoryDC::WriteDataToDC(CDC* pDC, int startx, int starty)
{
    ::SetDIBitsToDevice(pDC->m_hDC, 
				startx, 
				starty,
				m_DIBInfo.bmiHeader.biWidth,
				m_DIBInfo.bmiHeader.biHeight,
				0, 0, 0,
				m_DIBInfo.bmiHeader.biHeight,
				m_hImage, 
				&m_DIBInfo, 
				DIB_RGB_COLORS);
           			 
}

The function "WriteDataToDIBfile" in CGLMemoryDC allow to store DIB data to disk file

The use of CGLMemoryDC in application program to support printing is like

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void CGlprintView::OnDraw(CDC* pDC)
{
	CGlprintDoc* pDoc = GetDocument();
	ASSERT_VALID(pDoc);

	// TODO: add draw code for native data here
	//if print
	if(pDC->IsPrinting())
	{
		 //draw the image in memory DC to print DC 
		 CRect      drawRect;
		 int        cx, cy;
		 COLORREF	clrOld = pDC->SetTextColor(RGB(250, 10, 10));
		 pDC->TextOut(450,10, "This is a demo of OpenGL print provided by Zhaohui Xing");
		 pDC->SetTextColor(RGB(128, 128, 255));
		 pDC->TextOut(40,80, "Large Size");
		 drawRect.SetRect(40, 160, 2440, 1960);
		 pDC->DPtoLP(&drawRect);
		 m_MemImageDC.CopyDataToDC(pDC, drawRect);
		 pDC->TextOut(40,1960, "Medium Size");
		 drawRect.SetRect(500, 2040, 2100, 3240);
		 pDC->DPtoLP(&drawRect);
		 m_MemImageDC.CopyDataToDC(pDC, drawRect);
		 pDC->TextOut(40,3260, "Orignal Size");
		 m_MemImageDC.GetMemorySize(&cx, &cy);
		 drawRect.SetRect(1000, 3400, 1000 + cx , 3400 + cy);
		 pDC->DPtoLP(&drawRect);
		 m_MemImageDC.CopyDataToDC(pDC, drawRect);
		 pDC->SetTextColor(clrOld);
	}
	else //draw opnGL in current DC
	{
		 CPalette* oldPalette;

		 //Set logic palette
		 oldPalette = m_pDC->SelectPalette(&m_Palette, FALSE);
		 m_pDC->RealizePalette();
	
		 //draw openGL object
		 wglMakeCurrent(m_pDC->GetSafeHdc(), m_hRC);
		 DrawObject();
		 SwapBuffers(m_pDC->GetSafeHdc());
		 wglMakeCurrent(m_pDC->GetSafeHdc(), NULL);
		 
		 //Prepare the memory DC 
		 CRect rect;
		 GetClientRect(&rect);
		 m_MemImageDC.SetMemorySize(rect.Width(), rect.Height());
		 //copy the image data in current DC to memory
		 m_MemImageDC.CopyDataFromDC(m_pDC, rect);

		 m_pDC->SelectPalette(oldPalette, FALSE);
	}	     
}